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I use a MacBook Pro Retina 13-inch as my primary Mac and love it. Until shortly after the time the OS X 10.8.4 update came out, that is. Almost immediately after installing 10.8.4 the fans in my rMBP would run at almost top speed every waking minute. Needless to say, excessive fan noise is extremely distracting and it got to the point where I couldn't hear the TV over the blaring fans in my MacBook.
Point of order: According to a Genius at my local Apple Store, the fans in all MacBooks run any time that it is powered up, but at a very low (and quiet) speed. The fans increase in speed as more CPU cycles are used and when the temperature rises.
To troubleshoot the noisy fans, I opened Activity Monitor and sorted by the column labeled "% CPU" to identify any runaway applications, which can shorten battery runtime, affect performance, and increase heat and fan activity, as documented in Apple knowledge base article TS1473.
I identified a process called "udb" that only spawned when my rMBP was connected to a Thunderbolt display. It immediately pegged the CPU at over 100 percent and kicked the fans into overdrive. Voila!
The problem is that simply killing the process didn't help, it would immediately respawn and peg the CPU. The Genius at my local Apple Store narrowed "udb" down to something to do with iCloud syncing. Signing out of iCloud (in System Preferences) effectively killed the runaway "udb" process, but wasn't sustainable long term as a I use iCloud on a daily basis for Mail, Contacts, Calendars and Photo Stream.
The solution was to sign back into iCloud and uncheck all the options. With Activity Monitor open, we slowly turned on iCloud sync items one at a time, and everything was going great (i.e. no runaway processes) until we checked the box for "Documents & Data."
As soon as we checked the box for "Documents & Data" the udb process spawned and jumped to the top of the "% CPU" list and the fans kicked on. Unchecking "Documents & Data" made the process go away and the fans spin at a much more reasonable (and quieter) speed.
I really don't use "Documents & Data" iCloud syncing on OS X (while I do on my iOS devices) so I'm ok with leaving it turned off for the time being, but the genius suggested that it could be a corrupt iWork file that iCloud is trying to sync. He suggested that if I wanted to turn it back on, to download all my iCloud documents, delete them from iCloud and slowly put them back, while watching Activity Monitor for runaway processes.